In 1957, Kirsch's group developed a digital image scanner, to “trace variations of intensity over the surfaces of photographs”, and made the first digital scans. One of the first photographs scanned,[6] a picture of Kirsch’s three-month-old son, was captured as just 30,976 pixels, a 176 × 176 array, in an area measuring 5 cm × 5 cm.[7] The bit depth was only one bit per pixel, stark black and white with no intermediate shades of gray, but by combining several scans made using different scanning thresholds, grayscale information could also be acquired.[6] They used the computer to extract line drawings, count objects, recognize alphanumeric characters and produce oscilloscope displays.[7] Kirsch also proposed the Kirsch operator for edge detection.